Dynamat (Or Brown Bread from B-Quiet if you don't want to pay the outrageous prices of Dynamat) will really help with sound rattles. In the areas where the Dynamat isn't the best option, like where two plastic panels meet, some felt will do the trick.
In my case, I don't hear rattles because the music drowns what little there are, out.
As far as a head unit, I'v got an Alpine and really like it.